I recently had a friend ask me for sources that he could buy wildflower seed and sunflowers for an acre plot he wants to fill up. Folks, that is a lot of seed!
You will find wildflower seed is probably more expensive that you think, but I've written a little about it with some sources at http://www.mybedfordcounty.com/Flowers.html
Many of the wildflower seed sites you go to will have extra information about choosing and growing so be sure to check them out closely. If they have a "site map" they will have it laid out in outline form and is easier (at least for me) to find things.